Can BTC switch to PoS in the future and remaining safe at the same time?
No, bitcoin would never switch to proof of stake, that would be 100 steps backward for the network, proof of stake consensus algorithm also promotes centralization, we can agree that it is not the best for a decentralized network.
Bitcoin functions just fine the way it is now, and some of the things you read about it in the mainstream media is just propaganda published to discourage people from using and supporting bitcoin.